An airbag system comprises an airbag ECU (Electronic Control Unit) and side-direction G sensors for side-collision use (use in collisions in a side direction). The airbag ECU is provided at the center of the floor of a vehicle. The airbag ECU includes an embedded floor G sensor for side-collision use. The side-direction G sensors are provided on B pillars on both the vehicle-width-direction sides of the vehicle. Thus, there are a total of two side-direction G sensors.
In the event of a side collision, a signal from a side-direction G sensor for side-collision use and a signal from the floor G sensor for side-collision use are supplied to an AND operation. That is, when both moving average deviations of interval integrations of acceleration waveforms from the sensors exceed their respective threshold values, a collision-side curtain shield airbag apparatus or a side airbag apparatus is driven.
However, the airbag ECU includes not only the floor G sensor for side-collision use, but also an embedded floor G sensor for front-collision use (use in collisions in the forward direction). Thus, in the case of the airbag system, the size of the airbag ECU is inevitably large.
JP-A No. 9-240418 discloses an airbag system for driving a side airbag apparatus by using only a signal from a side-direction G sensor for side-collision use. In accordance with the airbag system described in this patent reference, it is not necessary to provide the airbag ECU with a floor G sensor for side-collision use. In this way, the airbag ECU can be made compact.
However, only a signal from a side-direction G sensor for side-collision use is used to determine whether the side airbag apparatus is to be driven or not to be driven. It is thus necessary to raise a threshold value to prevent the side airbag apparatus from operating when, for example, a small impact (such as a hammering shock) locally hits the side-direction G sensor for side-collision use. As a result, it is sometimes difficult to determine at an early stage whether or not a collision has occurred.